Problem 5 (20 points) Recall that the BCD number format use 4 bits to encode dig

Question

Problem 5 (20 points) Recall that the BCD number format use 4 bits to encode digits 0 to 9. We want to design a 2-digit BCD decrementer. Let al and a0 be two input BCD digits, and y1 and yo be two-digit BCD decrementing result. For example, if the inputs are 24 (i.e., a1-0010, a0-0100), the decrementor outputs will be 23 (i.e., y1-0010, yo-0011). If the inputs are 20 (i.e., a1-0010, a0-0000) the decrementor outputs will be 19 (i.e, y1-0001, yo-1001). The 00 and invalid inputs can be ignored. The input and output signals are . al, a0: 4-bit input in BCD format . yl, y0: 4-bit output in BCD format The entity declaration is 1ibrary leee: use ieee.std logic 1164.a11: use ieee.numeric std.all: entity bed_dec is portt al, a0: in std logic_vector (3 downto 0): yl, yo: out std logic_vector (3 downto 0) end bed_dec: Derive the architecture body.

Explanation / Answer

y1 = DIGITS-1;

a0 = VMAX;

while (y1 > 0)

{

    bcd[y1] = 0;

    while (a1 >= a0)

    {

        a1 = a1 - a0;

        bcd[i] = bcd[i] + 1;

    }

    a0 = a0 / 10;

    y1 = y0 - 1;

}

bcd[0] = a1;

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